Pedestal mounted rocker arm assemblies have a rocker arm rotatably mounted on a support pin which in turn is fixed to a cylinder head through a pedestal. The support pin is also known as a trunnion. Conventionally, the support pin rests on the pedestal, also known as a support block, which positions the overall rocker arm assembly away from the cylinder head. One end of the rocker arm is in contact with the push rod while the other end of the rocker arm is in contact with a valve shaft.
Roller bodies, also referred to as radial bearings, are conventionally used between the support pin and the rocker arm to facilitate rotational movement of the rocker arm on the support pin and to handle radial loads.
Moreover, an inner sleeve and an outer sleeve can be used. When incorporated into the rocker arm assembly, the inner sleeve and the outer sleeve are positioned between a through-hole in the rocker arm and the support pin is affixed within the inner sleeve. Furthermore, the rocker arm assembly can include rolling elements that are positioned between the inner sleeve and outer sleeve to accommodate radial loads.
Rocker arm assemblies can also be subject to axial forces or thrust forces. These axial forces occur when certain parts are out of alignment, for example, when the rocker arm pallet and the socket, the lower end of the push rod and the socket, or the valve shaft and the rocker arm pallet are out of alignment. Such rocker arm assemblies are often referred to as “offset rocker arm assemblies.”
To ensure the support pin, which typically has a flat upper surface and a concave lower surface that contacts the pedestal, does not become inverted prior to final installation a captured fastener is typically affixed in a centrally located bore in the support pin. Essentially, a captured fastener is a washer that has a circular flange extending from one side of the washer with threading on the inside of the flange. A bolt is also typically inserted in the captured fastener and bore prior to final assembly.
Rocker arm assemblies utilizing a captured fastener are known, see, for example, U.S. Pat. No. 6,694,936 and U.S. patent application No. 2008/0098971. Such rocker arms employ a captured fastener and a fastening bolt to ensure the support pin does not become inverted prior to final installation of the rocker arm to the engine. The use of the captured fastener and fastening bolt adds to the cost and packaging envelope of the rocker arm assembly. Also, in certain instances, captured fasteners cannot be used.
Additionally, see, for example, U.S. Pat. No. 5,437,209, which discloses a rocker arm assembly. The support pin of the rocker arm assembly has a D-shaped feature at each end to prevent the support pin from inverting. The support pin engages in a D-shaped hole stamped into the outer bearing cup, coupled with an inner bearing sleeve that has a specified range of diametric clearances to the support pin journal, preventing the support pin from inverting. The geometry required to achieve the D-shaped features on the support pin and associated components is complex, which adds to the overall cost and time required to manufacture the rocker arm components that incorporate the D-shaped feature.